1. Field Of The Invention
The present invention relates generally to the field of image correlating and pattern-recognition. More particularly, it relates to two-dimensional image correlation at video through-put rates.
2. Description Of The Prior Art
There are many applications where it is desirable to correlate an input image signal with a reference image. Such applications are becoming increasingly more common with increased automation. Image correlation is also often necessary where, because of space or environmental considerations, a human observer cannot be present. Also, it is often necessary that the correlation be performed in the fastest possible time. In many applications, the unknown incoming image is in the form of a video scanning signal. Therefore, it is desirable to perform the image correlation function at video through-put rates.
It is well known that optical information processing is powerful due to the fact that optical systems are capable of processing information in parallel at very high information rates with relatively few components. For example, a small missile capable of target recognition requires an image correlator that is relatively simple, is compact in size, requires little or no maintenance, is without mechanically moving parts and can perform "real-time" correlation, i.e. as fast as the optical input signal.
Previously, many correlating systems have the disadvantage of being basically one-dimensional in nature in that the input signal is compared sequentially with a reference. Of course, those skilled in the pertinent arts are aware that modern data processing equipment is capable of performing many real-time procedures through simultaneous parallel processing, or, simply extremely high speed. However, such systems are costly, complex, and generally large.
Some present automatic pattern recognition systems use extremely complicated optics, which are expensive, subject to vibration, and require precision placement. Other systems perform Fourier transformation of the data such transformation generally requires rather sophisticated data processing. Some present systems depend upon special coherent light sources, such as lasers. Coherent systems are highly sensitive to vibration and, therefore must be isolated from the environment in most practical applications. As a result, coherent light systems tend to be large in size and weight and are not easily used in environments such as those aboard ships or aircraft.
Incoherent optical correlation systems have been designed in the past. An example is illustrated in U.S. Pat. No. 3,937,942 to Bromley, incorporated herein by reference. The Bromley patent discloses a multi-channel optical correlation system employing a light source to illuminate a mask having a plurality of linearly disposed channels, each of which has recorded information defined by variations in opacity along its linear length. This system, however, provides only multiple one-dimensional correlations.
Additionally, some of the prior art systems using optical techniques utilize moving parts for performing comparisons. Moving parts are undesirably subject to vibration, acceleration forces, synchronization problems, and wear.
Other previous devices are designed to perform very specific functions, such as determining the speed of a vehicle or computing the radar ambiguity function.
Therefore, it is desirable to have a device that correlates an input image with a reference image at video through-put rates. It is further desirable that such a device be relatively simple and compact in size, be without mechanically moving parts, and not be dependent upon the use of coherent light.